The term unified network is used herein to describe a network comprising a plurality of interfaced networks. The unified network may include an internet, which may be a public or private network, and a plurality of other networks connected to each other via the internet. As an example, the unified network shown in FIGS. 1 and 2 includes a public network, eg. public internet (16), and one or more local or private networks, eg. intranets (18, 20, 22), with which the public network is interfaced. The private networks may be operated by small/medium enterprises, such as companies or academic institutions. In such unified networks, communications are made which cross boundaries between different networks. For example, a communication may be made between the different private networks (eg, between intranet (18) and intranet (20)) via a public network (eg. internet (16)) across the boundaries between the public and private networks. The communications are made between application aware devices which may be small end user gateways (4) or user equipments (2, 24), such as telephone devices, computing devices, video conferencing devices, etc. In order to support certain classes of communications between application aware devices across boundaries between different networks, signaling requests may need to be made requesting services from network infrastructure elements (6 to 10) in the communication path. The network infrastructure elements (6 to 10) may be routers or switches with inbuilt processing capabilities for provisioning the network services.
The private networks (18, 20, 22) may operate different applications from each other, for example for handling media transfer, and are likely to operate different applications from those, such as Internet Protocol (IP) used for handling media transport over the public network (16). In order that a communication can be made between networks, the network infrastructure elements at the boundaries of the networks, for example, elements (7, 8, 9 and 10) which interface a private network with the public network may have Network Address Translator (NAT) application software installed on them. In addition the network infrastructure elements located at the boundaries may also have Firewall application software installed on them for security purposes. For example, a firewall application can be used to ensure that only media having a network address known to the firewall application can enter the private network. Therefore, in a unified network the application aware devices terminating a communication path from a first network to a second network via a network boundary will not necessarily have an awareness of the intermediate network infrastructure elements over which the communication is to be carried.
This can mean that certain applications supported by the application aware devices will not work over such a communication path. As an example, the NAT application has the effect of interrupting communications for traffic types which include network address and transport port information in their payload, where this information is specific to a particular private network and so is not recognisable on other networks. Traffic types which might be interrupted by a NATs application include:                Voice over Internet (VoIP) control and peer messages (eg. ITU standard H284, Media Gateway Control Protocol (MGCP), ITU standard H323 and Session Initiation Protocol (SIP));        device management and administration protocols (eg. Simple Network Management Protocol (SNMP));        File Transfer Protocol (FTP) in certain cases;        VoIP quality report messages (RTCP);        Trivial File Transfer Protocol (TFTP) and        Domain Name System (DNS) protocol.        
In addition, automatic configuration servers (eg. operating using the Dynamic Host Configuration Protocol (DHCP)) may not operate when the servers are in the public network.
If such applications are to operate effectively over a unified network they need to be provided with certain network services. The type of services that need to be requested from the network infrastructure elements may include:                Pinhole opening, in particular packet filters need to be configured correctly to allow media flow traversal;        Bandwidth reservation, in particular for VoIP adequate bandwidth needs to be provided to support an acceptable voice quality; and/or        Network address translation. NATs is needed to provide addresses and ports in order to support proper reachability information to a remote application aware device in a different network.        
One signaling method for allocating network services which can be used is in-path signaling, as shown in FIG. 2. In accordance with in-path signaling, the terminating end points (2, 4) of a communication across the unified network themselves request the required network services required to support the communication from network infrastructure elements (6, 8, 10) along the communication path (12). The requests for services from the terminating end points travel along the communication path as shown by dotted line (14). This ensures that the resource allocated in response to the request for network services is provided along the communication path (12). A disadvantage with in-path signaling is that the terminating end points (2, 4) must have the capability of making the network service requests from infrastructure elements (6, 8, 10) along the communication path (12). This normally requires software to be implemented on the terminating end points, which can be costly, especially where the application aware devices (2, 4, 24) forming the terminal end points are already deployed in customer premises.
An alternative signaling method for allocating network services which can be used is off-path signaling, as shown in FIG. 3. In this case application servers or proxies (26, 28) located off a communications path (12) between terminating end points (2, 4) request the required network services required to support the communication on behalf of the terminating end points of the communication path. The application servers or proxies are control devices deployed on a network for providing the application aware devices (2, 4, 24) with a service, such as a voice service or a video service. For example, the application server (26, 28) may be a VoIP call agent for providing application aware devices with a voice service. However, where there are alternate communication paths across the network between terminating end points (for example a path via infrastructure elements (6, 7, 9) is an alternative to the communication path (12) via infrastructure elements (6, 8, 10)), the application servers or proxies (26, 28) may request network services from network infrastructure which is not on the actual communication path between the terminal end points. For example, application server or proxy (26) may incorrectly request resource from infrastructure (7) and application server or proxy (28) may incorrectly request resource from infrastructure (9). In this case the resource allocated in response to the requests for network services may not be resource on the communication path (12) with the result that there is insufficient resource on the communication path (12) to support the communication. Alternatively, the application servers or proxies (26, 28) may request network services from the infrastructure element on all possible communication paths between the terminating end points which is costly in terms of wasted resource. These problems become highly significant in complex networks or networks where dynamic changes are occurring.